package cn.leancloud.codec;

import java.io.UnsupportedEncodingException;

public class Base64 {
  /**
   * Default values for encoder/decoder flags.
   */
  public static final int DEFAULT = 0;

  /**
   * Encoder flag bit to omit the padding '=' characters at the end
   * of the output (if any).
   */
  public static final int NO_PADDING = 1;

  /**
   * Encoder flag bit to omit all line terminators (i.e., the output
   * will be on one long line).
   */
  public static final int NO_WRAP = 2;

  /**
   * Encoder flag bit to indicate lines should be terminated with a
   * CRLF pair instead of just an LF.  Has no effect if {@code
   * NO_WRAP} is specified as well.
   */
  public static final int CRLF = 4;

  /**
   * Encoder/decoder flag bit to indicate using the "URL and
   * filename safe" variant of Base64 (see RFC 3548 section 4) where
   * {@code -} and {@code _} are used in place of {@code +} and
   * {@code /}.
   */
  public static final int URL_SAFE = 8;

  /**
   * Flag to pass to {@link Base64OutputStream} to indicate that it
   * should not close the output stream it is wrapping when it
   * itself is closed.
   */
  public static final int NO_CLOSE = 16;

  //  --------------------------------------------------------
  //  shared code
  //  --------------------------------------------------------

  /* package */
  static abstract class Coder {
    public byte[] output;
    public int op;

    /**
     * Encode/decode another block of input data.  this.output is
     * provided by the caller, and must be big enough to hold all
     * the coded data.  On exit, this.opwill be set to the length
     * of the coded data.
     *
     * @param finish true if this is the final call to process for
     *        this object.  Will finalize the coder state and
     *        include any final bytes in the output.
     *
     * @return true if the input so far is good; false if some
     *         error has been detected in the input stream..
     */
    public abstract boolean process(byte[] input, int offset, int len, boolean finish);

    /**
     * @return the maximum number of bytes a call to process()
     * could produce for the given number of input bytes.  This may
     * be an overestimate.
     */
    public abstract int maxOutputSize(int len);
  }

  //  --------------------------------------------------------
  //  decoding
  //  --------------------------------------------------------

  /**
   * Decode the Base64-encoded data in input and return the data in
   * a new byte array.
   *
   * <p>The padding '=' characters at the end are considered optional, but
   * if any are present, there must be the correct number of them.
   *
   * @param str    the input String to decode, which is converted to
   *               bytes using the default charset
   * @param flags  controls certain features of the decoded output.
   *               Pass {@code DEFAULT} to decode standard Base64.
   *
   * @throws IllegalArgumentException if the input contains
   * incorrect padding
   */
  public static byte[] decode(String str, int flags) {
    return decode(str.getBytes(), flags);
  }

  /**
   * Decode the Base64-encoded data in input and return the data in
   * a new byte array.
   *
   * <p>The padding '=' characters at the end are considered optional, but
   * if any are present, there must be the correct number of them.
   *
   * @param input the input array to decode
   * @param flags  controls certain features of the decoded output.
   *               Pass {@code DEFAULT} to decode standard Base64.
   *
   * @throws IllegalArgumentException if the input contains
   * incorrect padding
   */
  public static byte[] decode(byte[] input, int flags) {
    return decode(input, 0, input.length, flags);
  }

  /**
   * Decode the Base64-encoded data in input and return the data in
   * a new byte array.
   *
   * <p>The padding '=' characters at the end are considered optional, but
   * if any are present, there must be the correct number of them.
   *
   * @param input  the data to decode
   * @param offset the position within the input array at which to start
   * @param len    the number of bytes of input to decode
   * @param flags  controls certain features of the decoded output.
   *               Pass {@code DEFAULT} to decode standard Base64.
   *
   * @throws IllegalArgumentException if the input contains
   * incorrect padding
   */
  public static byte[] decode(byte[] input, int offset, int len, int flags) {
    // Allocate space for the most data the input could represent.
    // (It could contain less if it contains whitespace, etc.)
    Decoder decoder = new Decoder(flags, new byte[len*3/4]);

    if (!decoder.process(input, offset, len, true)) {
      throw new IllegalArgumentException("bad base-64");
    }

    // Maybe we got lucky and allocated exactly enough output space.
    if (decoder.op == decoder.output.length) {
      return decoder.output;
    }

    // Need to shorten the array, so allocate a new one of the
    // right size and copy.
    byte[] temp = new byte[decoder.op];
    System.arraycopy(decoder.output, 0, temp, 0, decoder.op);
    return temp;
  }

  /* package */ static class Decoder extends Coder {
    /**
     * Lookup table for turning bytes into their position in the
     * Base64 alphabet.
     */
    private static final int DECODE[] = {
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 62, -1, -1, -1, 63,
            52, 53, 54, 55, 56, 57, 58, 59, 60, 61, -1, -1, -1, -2, -1, -1,
            -1,  0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11, 12, 13, 14,
            15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, -1, -1, -1, -1, -1,
            -1, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40,
            41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    };

    /**
     * Decode lookup table for the "web safe" variant (RFC 3548
     * sec. 4) where - and _ replace + and /.
     */
    private static final int DECODE_WEBSAFE[] = {
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 62, -1, -1,
            52, 53, 54, 55, 56, 57, 58, 59, 60, 61, -1, -1, -1, -2, -1, -1,
            -1,  0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11, 12, 13, 14,
            15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, -1, -1, -1, -1, 63,
            -1, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40,
            41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    };

    /** Non-data values in the DECODE arrays. */
    private static final int SKIP = -1;
    private static final int EQUALS = -2;

    /**
     * States 0-3 are reading through the next input tuple.
     * State 4 is having read one '=' and expecting exactly
     * one more.
     * State 5 is expecting no more data or padding characters
     * in the input.
     * State 6 is the error state; an error has been detected
     * in the input and no future input can "fix" it.
     */
    private int state;   // state number (0 to 6)
    private int value;

    final private int[] alphabet;

    public Decoder(int flags, byte[] output) {
      this.output = output;

      alphabet = ((flags & URL_SAFE) == 0) ? DECODE : DECODE_WEBSAFE;
      state = 0;
      value = 0;
    }

    /**
     * @return an overestimate for the number of bytes {@code
     * len} bytes could decode to.
     */
    public int maxOutputSize(int len) {
      return len * 3/4 + 10;
    }

    /**
     * Decode another block of input data.
     *
     * @return true if the state machine is still healthy.  false if
     *         bad base-64 data has been detected in the input stream.
     */
    public boolean process(byte[] input, int offset, int len, boolean finish) {
      if (this.state == 6) return false;

      int p = offset;
      len += offset;

      // Using local variables makes the decoder about 12%
      // faster than if we manipulate the member variables in
      // the loop.  (Even alphabet makes a measurable
      // difference, which is somewhat surprising to me since
      // the member variable is final.)
      int state = this.state;
      int value = this.value;
      int op = 0;
      final byte[] output = this.output;
      final int[] alphabet = this.alphabet;

      while (p < len) {
        // Try the fast path:  we're starting a new tuple and the
        // next four bytes of the input stream are all data
        // bytes.  This corresponds to going through states
        // 0-1-2-3-0.  We expect to use this method for most of
        // the data.
        //
        // If any of the next four bytes of input are non-data
        // (whitespace, etc.), value will end up negative.  (All
        // the non-data values in decode are small negative
        // numbers, so shifting any of them up and or'ing them
        // together will result in a value with its top bit set.)
        //
        // You can remove this whole block and the output should
        // be the same, just slower.
        if (state == 0) {
          while (p+4 <= len &&
                  (value = ((alphabet[input[p] & 0xff] << 18) |
                          (alphabet[input[p+1] & 0xff] << 12) |
                          (alphabet[input[p+2] & 0xff] << 6) |
                          (alphabet[input[p+3] & 0xff]))) >= 0) {
            output[op+2] = (byte) value;
            output[op+1] = (byte) (value >> 8);
            output[op] = (byte) (value >> 16);
            op += 3;
            p += 4;
          }
          if (p >= len) break;
        }

        // The fast path isn't available -- either we've read a
        // partial tuple, or the next four input bytes aren't all
        // data, or whatever.  Fall back to the slower state
        // machine implementation.

        int d = alphabet[input[p++] & 0xff];

        switch (state) {
          case 0:
            if (d >= 0) {
              value = d;
              ++state;
            } else if (d != SKIP) {
              this.state = 6;
              return false;
            }
            break;

          case 1:
            if (d >= 0) {
              value = (value << 6) | d;
              ++state;
            } else if (d != SKIP) {
              this.state = 6;
              return false;
            }
            break;

          case 2:
            if (d >= 0) {
              value = (value << 6) | d;
              ++state;
            } else if (d == EQUALS) {
              // Emit the last (partial) output tuple;
              // expect exactly one more padding character.
              output[op++] = (byte) (value >> 4);
              state = 4;
            } else if (d != SKIP) {
              this.state = 6;
              return false;
            }
            break;

          case 3:
            if (d >= 0) {
              // Emit the output triple and return to state 0.
              value = (value << 6) | d;
              output[op+2] = (byte) value;
              output[op+1] = (byte) (value >> 8);
              output[op] = (byte) (value >> 16);
              op += 3;
              state = 0;
            } else if (d == EQUALS) {
              // Emit the last (partial) output tuple;
              // expect no further data or padding characters.
              output[op+1] = (byte) (value >> 2);
              output[op] = (byte) (value >> 10);
              op += 2;
              state = 5;
            } else if (d != SKIP) {
              this.state = 6;
              return false;
            }
            break;

          case 4:
            if (d == EQUALS) {
              ++state;
            } else if (d != SKIP) {
              this.state = 6;
              return false;
            }
            break;

          case 5:
            if (d != SKIP) {
              this.state = 6;
              return false;
            }
            break;
        }
      }

      if (!finish) {
        // We're out of input, but a future call could provide
        // more.
        this.state = state;
        this.value = value;
        this.op = op;
        return true;
      }

      // Done reading input.  Now figure out where we are left in
      // the state machine and finish up.

      switch (state) {
        case 0:
          // Output length is a multiple of three.  Fine.
          break;
        case 1:
          // Read one extra input byte, which isn't enough to
          // make another output byte.  Illegal.
          this.state = 6;
          return false;
        case 2:
          // Read two extra input bytes, enough to emit 1 more
          // output byte.  Fine.
          output[op++] = (byte) (value >> 4);
          break;
        case 3:
          // Read three extra input bytes, enough to emit 2 more
          // output bytes.  Fine.
          output[op++] = (byte) (value >> 10);
          output[op++] = (byte) (value >> 2);
          break;
        case 4:
          // Read one padding '=' when we expected 2.  Illegal.
          this.state = 6;
          return false;
        case 5:
          // Read all the padding '='s we expected and no more.
          // Fine.
          break;
      }

      this.state = state;
      this.op = op;
      return true;
    }
  }

  //  --------------------------------------------------------
  //  encoding
  //  --------------------------------------------------------

  /**
   * Base64-encode the given data and return a newly allocated
   * String with the result.
   *
   * @param input  the data to encode
   * @param flags  controls certain features of the encoded output.
   *               Passing {@code DEFAULT} results in output that
   *               adheres to RFC 2045.
   */
  public static String encodeToString(byte[] input, int flags) {
    try {
      return new String(encode(input, flags), "US-ASCII");
    } catch (UnsupportedEncodingException e) {
      // US-ASCII is guaranteed to be available.
      throw new AssertionError(e);
    }
  }

  /**
   * Base64-encode the given data and return a newly allocated
   * String with the result.
   *
   * @param input  the data to encode
   * @param offset the position within the input array at which to
   *               start
   * @param len    the number of bytes of input to encode
   * @param flags  controls certain features of the encoded output.
   *               Passing {@code DEFAULT} results in output that
   *               adheres to RFC 2045.
   */
  public static String encodeToString(byte[] input, int offset, int len, int flags) {
    try {
      return new String(encode(input, offset, len, flags), "US-ASCII");
    } catch (UnsupportedEncodingException e) {
      // US-ASCII is guaranteed to be available.
      throw new AssertionError(e);
    }
  }

  /**
   * Base64-encode the given data and return a newly allocated
   * byte[] with the result.
   *
   * @param input  the data to encode
   * @param flags  controls certain features of the encoded output.
   *               Passing {@code DEFAULT} results in output that
   *               adheres to RFC 2045.
   */
  public static byte[] encode(byte[] input, int flags) {
    return encode(input, 0, input.length, flags);
  }

  /**
   * Base64-encode the given data and return a newly allocated
   * byte[] with the result.
   *
   * @param input  the data to encode
   * @param offset the position within the input array at which to
   *               start
   * @param len    the number of bytes of input to encode
   * @param flags  controls certain features of the encoded output.
   *               Passing {@code DEFAULT} results in output that
   *               adheres to RFC 2045.
   */
  public static byte[] encode(byte[] input, int offset, int len, int flags) {
    Encoder encoder = new Encoder(flags, null);

    // Compute the exact length of the array we will produce.
    int output_len = len / 3 * 4;

    // Account for the tail of the data and the padding bytes, if any.
    if (encoder.do_padding) {
      if (len % 3 > 0) {
        output_len += 4;
      }
    } else {
      switch (len % 3) {
        case 0: break;
        case 1: output_len += 2; break;
        case 2: output_len += 3; break;
      }
    }

    // Account for the newlines, if any.
    if (encoder.do_newline && len > 0) {
      output_len += (((len-1) / (3 * Encoder.LINE_GROUPS)) + 1) *
              (encoder.do_cr ? 2 : 1);
    }

    encoder.output = new byte[output_len];
    encoder.process(input, offset, len, true);

    assert encoder.op == output_len;

    return encoder.output;
  }

  /* package */ static class Encoder extends Coder {
    /**
     * Emit a new line every this many output tuples.  Corresponds to
     * a 76-character line length (the maximum allowable according to
     * <a href="http://www.ietf.org/rfc/rfc2045.txt">RFC 2045</a>).
     */
    public static final int LINE_GROUPS = 19;

    /**
     * Lookup table for turning Base64 alphabet positions (6 bits)
     * into output bytes.
     */
    private static final byte ENCODE[] = {
            'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P',
            'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f',
            'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v',
            'w', 'x', 'y', 'z', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '+', '/',
    };

    /**
     * Lookup table for turning Base64 alphabet positions (6 bits)
     * into output bytes.
     */
    private static final byte ENCODE_WEBSAFE[] = {
            'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P',
            'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f',
            'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v',
            'w', 'x', 'y', 'z', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '-', '_',
    };

    final private byte[] tail;
    /* package */ int tailLen;
    private int count;

    final public boolean do_padding;
    final public boolean do_newline;
    final public boolean do_cr;
    final private byte[] alphabet;

    public Encoder(int flags, byte[] output) {
      this.output = output;

      do_padding = (flags & NO_PADDING) == 0;
      do_newline = (flags & NO_WRAP) == 0;
      do_cr = (flags & CRLF) != 0;
      alphabet = ((flags & URL_SAFE) == 0) ? ENCODE : ENCODE_WEBSAFE;

      tail = new byte[2];
      tailLen = 0;

      count = do_newline ? LINE_GROUPS : -1;
    }

    /**
     * @return an overestimate for the number of bytes {@code
     * len} bytes could encode to.
     */
    public int maxOutputSize(int len) {
      return len * 8/5 + 10;
    }

    public boolean process(byte[] input, int offset, int len, boolean finish) {
      // Using local variables makes the encoder about 9% faster.
      final byte[] alphabet = this.alphabet;
      final byte[] output = this.output;
      int op = 0;
      int count = this.count;

      int p = offset;
      len += offset;
      int v = -1;

      // First we need to concatenate the tail of the previous call
      // with any input bytes available now and see if we can empty
      // the tail.

      switch (tailLen) {
        case 0:
          // There was no tail.
          break;

        case 1:
          if (p+2 <= len) {
            // A 1-byte tail with at least 2 bytes of
            // input available now.
            v = ((tail[0] & 0xff) << 16) |
                    ((input[p++] & 0xff) << 8) |
                    (input[p++] & 0xff);
            tailLen = 0;
          };
          break;

        case 2:
          if (p+1 <= len) {
            // A 2-byte tail with at least 1 byte of input.
            v = ((tail[0] & 0xff) << 16) |
                    ((tail[1] & 0xff) << 8) |
                    (input[p++] & 0xff);
            tailLen = 0;
          }
          break;
      }

      if (v != -1) {
        output[op++] = alphabet[(v >> 18) & 0x3f];
        output[op++] = alphabet[(v >> 12) & 0x3f];
        output[op++] = alphabet[(v >> 6) & 0x3f];
        output[op++] = alphabet[v & 0x3f];
        if (--count == 0) {
          if (do_cr) output[op++] = '\r';
          output[op++] = '\n';
          count = LINE_GROUPS;
        }
      }

      // At this point either there is no tail, or there are fewer
      // than 3 bytes of input available.

      // The main loop, turning 3 input bytes into 4 output bytes on
      // each iteration.
      while (p+3 <= len) {
        v = ((input[p] & 0xff) << 16) |
                ((input[p+1] & 0xff) << 8) |
                (input[p+2] & 0xff);
        output[op] = alphabet[(v >> 18) & 0x3f];
        output[op+1] = alphabet[(v >> 12) & 0x3f];
        output[op+2] = alphabet[(v >> 6) & 0x3f];
        output[op+3] = alphabet[v & 0x3f];
        p += 3;
        op += 4;
        if (--count == 0) {
          if (do_cr) output[op++] = '\r';
          output[op++] = '\n';
          count = LINE_GROUPS;
        }
      }

      if (finish) {
        // Finish up the tail of the input.  Note that we need to
        // consume any bytes in tail before any bytes
        // remaining in input; there should be at most two bytes
        // total.

        if (p-tailLen == len-1) {
          int t = 0;
          v = ((tailLen > 0 ? tail[t++] : input[p++]) & 0xff) << 4;
          tailLen -= t;
          output[op++] = alphabet[(v >> 6) & 0x3f];
          output[op++] = alphabet[v & 0x3f];
          if (do_padding) {
            output[op++] = '=';
            output[op++] = '=';
          }
          if (do_newline) {
            if (do_cr) output[op++] = '\r';
            output[op++] = '\n';
          }
        } else if (p-tailLen == len-2) {
          int t = 0;
          v = (((tailLen > 1 ? tail[t++] : input[p++]) & 0xff) << 10) |
                  (((tailLen > 0 ? tail[t++] : input[p++]) & 0xff) << 2);
          tailLen -= t;
          output[op++] = alphabet[(v >> 12) & 0x3f];
          output[op++] = alphabet[(v >> 6) & 0x3f];
          output[op++] = alphabet[v & 0x3f];
          if (do_padding) {
            output[op++] = '=';
          }
          if (do_newline) {
            if (do_cr) output[op++] = '\r';
            output[op++] = '\n';
          }
        } else if (do_newline && op > 0 && count != LINE_GROUPS) {
          if (do_cr) output[op++] = '\r';
          output[op++] = '\n';
        }

        assert tailLen == 0;
        assert p == len;
      } else {
        // Save the leftovers in tail to be consumed on the next
        // call to encodeInternal.

        if (p == len-1) {
          tail[tailLen++] = input[p];
        } else if (p == len-2) {
          tail[tailLen++] = input[p];
          tail[tailLen++] = input[p+1];
        }
      }

      this.op = op;
      this.count = count;

      return true;
    }
  }

  private Base64() { }   // don't instantiate
}
